New Stable and Fast Ring-Polymer Molecular Dynamics for Calculating Bimolecular Rate Coefficients with Example of OH + CH_4

Predictive model of polymer reaction kinetics and coagulation behavior in seeded emulsion co- and ter-polymerizations

A mathematical model to describe the emulsion polymerization kinetics of co- and ter-polymerizations is developed. The model is based on the classical Smith-Ewart (SE) equations, within the pseudo-homopolymerization approach, with state-of-the-art models for radical entry and desorption. For co- and ter-polymerizations there are unknown parameters in the model which are related to monomer-specific gel-effect coefficients, that are needed to compute the bimolecular termination reaction rates. The unknown parameters are determined through extensive calibration of the model on literature data for…

Assessing Parameters for Ring Polymer Molecular Dynamics Simulations at Low Temperatures: DH+H Chemical Reaction

Ring polymer molecular dynamics (RPMD) is an accurate method for calculating thermal chemical reaction rates. It has recently been discovered that low-temperature calculations are strongly affected by the simulation parameters. Here, for the thermally activated reaction DH + H -> D + H2, we calculate the RPMD rate constants at T = 50, 100, and 300 K and demonstrate that for T >= 100 K the standard input parameters yield accurate results, but at low temperatures (e.g., 50 K) one must increase the asymptotic distance and force constant, and decrease the umbrella integration step.

迈向可靠的热速率常数计算：用于 OH + HBr → Br + H₂O 反应的环聚合物分子动力学

Towards reliable calculations of thermal rate constants: ring polymer molecular dynamics for the OH + HBr $\to$ Br + H$_2$O reaction

该研究结合 MTP 与 RPMD，并利用主动学习构建训练集，计算 OH + HBr 反应热速率常数；在 200–500 K 范围内，结果较 QCT 更接近实验值。

用于精确隧穿分裂的微扰修正环聚合物瞬子理论

Perturbatively corrected ring-polymer instanton theory for accurate tunneling splittings

本文提出环聚合物瞬子微扰修正方法RPI+PC，通过计算高阶渐近项并利用势能高阶导数纳入非谐效应，在丙二醛及其氘代衍生物中显著降低隧穿分裂计算误差，兼顾精度与效率。

Divide-and-Conquer Method for Instanton Rate Theory

Ring-polymer instanton theory has been developed to simulate the quantum dynamics of molecular systems at low temperatures. Chemical reaction rates can be obtained by locating the dominant tunneling pathway and analyzing fluctuations around it. In the standard method, calculating the fluctuation terms involves the diagonalization of a large matrix, which can be unfeasible for large systems with a high number of ring-polymer beads. Here we present a method for computing the instanton fluctuations with a large reduction in computational scaling. This method is applied to three reactions describe…

Modeling of stimuli-responsive nanoreactors: rational rate control towards the design of colloidal enzymes

In modern applications of heterogeneous liquid-phase nanocatalysis, the catalysts (e.g., metal nanoparticles) need to be typically affixed to a colloidal carrier system for stability and easy handling. "Passive carriers" (e.g., simple polyelectrolytes) serve for a controlled synthesis of the nanoparticles and prevent coagulation during catalysis. Recently, however, hybrid conjugates of nanoparticles and synthetic thermosensitive polymers have been developed that enable to change the catalytic activity of the nanoparticles by external triggers. In particular, nanoparticles embedded in a stimuli…

Ring Polymer Molecular Dynamics and Active Learning of Moment Tensor Potential for Gas-Phase Barrierless Reactions: Application to S + H2

Ring polymer molecular dynamics (RPMD) has proven to be an accurate approach for calculating thermal rate coefficients of various chemical reactions. For wider application of this methodology, efficient ways to generate the underlying full-dimensional potential energy surfaces (PESs) and the corresponding energy gradients are required. Recently, we have proposed a fully automated procedure based on combining the original RPMDrate code with active learning for PES on-the-fly using moment tensor potential and successfully applied it to two representative thermally activated chemical reactions [I…

Quantum dynamics of the Li+HF-->H+LiF reaction at ultralow temperatures

Quantum mechanical calculations are reported for the Li+HF(v=0,1,j=0)-->H+LiF(v',j') bimolecular scattering process at low and ultralow temperatures. Calculations have been performed for zero total angular momentum using a recent high accuracy potential energy surface for the X 2A' electronic ground state. For Li+HF(v=0,j=0), the reaction is dominated by resonances due to the decay of metastable states of the Li...F-H van der Waals complex. Assignment of these resonances has been carried out by calculating the eigenenergies of the quasibound states. We also find that while chemical reactivity …

用于非对称势阱间隧穿的环聚合物瞬子理论

Ring-polymer instanton theory for tunneling between asymmetric wells

针对原始瞬子理论无法计算非对称双势阱隧穿裂分的问题，提出基于投影通量关联函数的新公式，经模型验证精度较高，成功应用于α-葑醇隧穿研究并厘清隧穿裂分与反应速率的关系。

Automated Calculation of Thermal Rate Coefficients using Ring Polymer Molecular Dynamics and Machine-Learning Interatomic Potentials with Active Learning

We propose a methodology for fully automated calculation of thermal rate coefficients of gas phase chemical reactions, which is based on combining the ring polymer molecular dynamics (RPMD) with the machine-learning interatomic potentials actively learning on-the-fly. Based on the original computational procedure implemented in the RPMDrate code, our methodology gradually and automatically constructs the potential energy surfaces (PESs) from scratch with the data set points being selected and accumulated during the RPMDrate simulation. Such an approach ensures that our final machine-learning m…

Efficient dynamical correction of the transition state theory rate estimate for a flat energy barrier

The recrossing correction to the transition state theory estimate of a thermal rate can be difficult to calculate when the energy barrier is flat. This problem arises, for example, in polymer escape if the polymer is long enough to stretch between the initial and final state energy wells while the polymer beads undergo diffusive motion back and forth over the barrier. We present an efficient method for evaluating the correction factor by constructing a sequence of hyperplanes starting at the transition state and calculating the probability that the system advances from one hyperplane to anothe…

基于振动模式的非仿射理论计算聚合物熔体的粘度

Viscosity of polymer melts using non-affine theory based on vibrational modes

本研究应用非仿射晶格动力学（NALD）和瞬态简正模分析方法计算Kremer-Grest聚合物系统在不同温度下的粘度，发现所有振动模式均对粘度有贡献，为玻璃化转变附近等系统提供了高效粘度计算框架。